Stimulation of secretory IgA and secretory component of immunoglobulins in small intestine of rats treated withSaccharomyces boulardii

Abstract

Saccharomyces boulardii (S.b.) is largely used in Western European countries for the treatment of acute infectious enteritis and antibiotic-induced gastrointestinal disorders. To study the mechanisms of the protective effect of S.b. against enteral pathogen infection, we assessed the response of the intestinal secretion of secretory IgA (s-IgA) and of the secretory component of immunoglobulins (SC) to oral administration of high doses (0.5 mg/g body weight, three times per day) of S.b. cells in growing rats. S.b. cells (biological activity: 2.8× 109 viable cells/100 mg) were administered daily by gastric intubation to weanling rats from day 14 until day 22 postpartum. Control groups received either 0.9% saline or ovalbumin following the same schedule. Expressed per milligram of cell protein, SC content was significantly increased in crypt cells isolated from the jejunum (48.5% vs saline controls, P< 0.05) as it was in the duodenal fluid (62.8% vs saline controls, P<0.01) of rats treated with S.b. Oral treatment with S.b. had no effect on the secretion of SC by the liver. In the duodenal fluid of rats treated with S.b. cells, the mean concentration of s-IgA was increased by 56.9% (P<0.01) over the concentration of s-IgA measured in saline controls. Compared to control rats treated from day 14 until day 22 postpartum with an antigenic load of ovalbumin equivalent to the total protein load provided by Sb cells (0.05 mg protein/g body weight, three times per day), S.b.-treated rats also exhibited a significantly higher intestinal concentration of SC (69% in villus cells, P<0.025 and 80% in crypt cells, P<0.01 These changes in intestinal SC and s-IgA concentration appeared not to be due to an increase in enterocyte turnover rate, since the mucosal mass parameters and the incorporation rate of [3H]thymidine into DNA measured in the jejunum, ileum, and colon remained unchanged in S.b.- treated rats. Our findings suggest that one of the mechanisms by which S.b. exerts its immunoprotective effect in the gastrointestinal tract is a stimulation of the intestinal secretion of s-IgA and of the secretory component of immunoglobulins.